1. Field of the Invention
The present invention pertains to textured yarn and, more particularly, to such yarn having a crimp with marked cusps and a process of manufacturing the same.
2. Discussion of the Prior Art
It is a necessity in the textile industry to include a drawing step with structural modification of the filaments when processing continuous filament thermoplastic yarns. Indeed, if the yarn is not drawn or is insufficiently drawn, it is essentially useless for the production of fabric since drawable yarn is brittle and lacks elasticity. The necessity of drawing seems to be by-passed in few cases, when fully drawn yarn is obtained directly below the spinnerette. But, even in such cases, the drawing step is performed "on-line" to obtain appropriate orientation of the polymer macromolecules. The drawing is thus performed by very expensive apparatus installed below the spinnerette which operates at very high speeds in the range of 3,000 m/min or more on each single strand of flat yarn. The resulting product is only flat yarn, for which the subsequent processing step may be texturizing, which is necessarily performed by other machines. Normal texturizing is a very slow process operating in the range of 200 m/min on each single strand or yarn. After texturizing, the product has a much greater commercial value.
The most widely used approach to drawing now practiced in industry is the use of drawtwisters; i.e., the use of machines located after and apart from the spinning apparatus. On drawtwisters, each strand of yarn is separately drawn over a drawing rod, and many rods are installed side-by-side on a general frame. Generally, each yarn being drawn advances through an upstream set of rollers at a speed related to the draw ratio, and exits from a downstream set of rollers at a higher speed of approximately 1,000 m/min. Each yarn is then taken up on bobbins or, more generally, on pirns which have a peripheral speed matching the exit speed of the yarn. The resulting product is flat yarn, for which the subsequent processing step may be texturizing, as above.
In some cases, the above-cited drawing is directly combined on-line with false-twist texturizing. The false-twist equipment is then placed on a common frame directly after the above-cited downstream set of rollers. The exit speed of the yarn is then limited by the texturizing part to approximately 200 m/min, and the resulting product is texturized yarn.
Another approach to drawing yarn is disclosed in U.S. Pat. No. 3,568,278, issued to Mattingly. In Mattingly, a filament of undrawn yarn is stitched into a chain of loops in which three sections of the yarn extend between each pair of loop bites. The yarn is then drawn while arranged as a chain of loops to produce drawn yarn having crimps formed at the bite of each loop. The chain of loops is then deknitted, and the resulting strand of yarn is bulked by passing the yarn over a sharp edge or through an air blast stream after deknitting. The resulting product is then a flat yarn with scattered crimps (or cusps) and cannot be used nor presented as a texturized yarn without further treatment being applied to each strand of yarn. Further texturizing treatment is not disclosed in the Mattingly process.
The process disclosed by Mattingly is of limited economic feasibility and has not been generally adopted due to the poor bulk quality of the product and due to a poor production rate per strand of yarn. Indeed, since the process is necessarily realized on-line from undrawn to bulked yarn for each single strand of yarn, the exit speed (i.e., the matching take-up speed of the yarn) limits the production rate to a level equivalent to the level of the above-cited drawtwisters. The fact that three sections of yarn are in parallel array during the drawing has no influence on the production rate.
In addition, the subsequent crimping step or overcrimping step occurring after deknitting would be performed on a single strand of yarn moving at a speed of 1,000 m/min, and it is doubtful that the technology for accomplishing this crimping at such a speed exists. Furthermore, it is well known that it is difficult to economically crimp a single strand of yarn. It is thereby concluded that stitching yarn into a single row of stitches, as taught by Mattingly, does not offer an economical alternative to the widely used afore-described methods in which strands of yarn are drawn in parallel and texturized in parallel or are draw-texturized in parallel.
The prior art also includes U.S. Pat. No. 3,305,911 issued to Chapman et al. which discloses the concept of knitting undrawn yarn into a tubular fabric and then drawing the fabric to produce a fabric of drawn yarn having crimps therein. Chapman et al. is, however, not concerned with a knit-deknit process for producing individual strands of yarn. Consequently, Chapman et al. is not confronted with the problem of deknitting drawn yarn from a fabric, the yarn of which fabric has been crimped by drawing the fabric.
Bulking of yarn is an additional consideration and it is well known to modify the bulk and/or the extensibility of continuous filament thermoplastic yarns through various mechanical processes by deforming the yarns, the deformation being simultaneously or subsequently set through an appropriate heat treatment. Attempts have been made, for example, to deform a bundle of filaments either by means of a false twist spindle or by passage over a sharp edge in order to produce a three-dimensional helicoidal crimp, or by passage into a gear mechanism or by packing into a so-called "stuffer box" in order to produce a flat three-dimensional crimp.
Another well known mechanical process consists of knitting drawn yarn in the form of a flat knit or a tube, heat setting the knitted fabric and finally deknitting or unraveling the yarn. This method, which is returning to popularity, is often called KDK (Knit-Deknit), or knitting-setting-deknitting. The textured yarns obtained with this process, sometimes called "crinkle" yarns are characterized by a substantially flat crimp having a deep sinusoidal configuration. These yarns, which are used particularly in hosiery and for manufacturing footwear and sweaters, often lack elasticity; and, moreover, due to the configuration of the crimp, the articles woven or knitted from these yarns present a defective appearance primarily caused by synchronism of yarn deformation. To improve crimp regularity and the elasticity of such yarns, it has been proposed to heatset the knit while maintaining it under regulated tension. The yarns thus obtained show marked loops, separated by essentially parallel yarn portions, and have increased internal crimp characteristics.
With the packing or compression mechanical texturing process mentioned above, it has been proposed to modify the voluminocity of thermoplastic yarns by compressing the yarns in a special box, referred to as a stuffing or packing box, and simultaneously or subsequently setting the deformation thus produced in the yarn. yarns produced by such process have a characteristic crimp, called a straight serrated crimp, i.e., in the shape of a more-or-less open V. The latter process, however, which is well known, still has certain disadvantages since it cannot be easily applied to a single strand of yarn of average count, and is even more difficult to apply to yarn of low count. As a result, the yarn obtained not only lacks bulk and elasticity, but the production cost is very high. This is particularly so for the yarns for textile end uses.